If you were to broadcast a message of about ten to fifteen words into space to be received by alien civilizations, what would you say?
With such a short message length, I would just say:
"2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31".
This would tell them a lot about us. It would say "we exist", "We are at this location" and "we are technologically able to send messages".
If we tried to send a more complex message it might not be interpreted as a message. But sending the first 11 prime numbers would be universal and most importantly it is an obvious message and could not be mistaken for something natural or accidental.
Some people might argue that we have been sending messages for about 100 years already because every radio and TV signal and cell phone call and radar pulse is radiated into space where it will travel forever. Yes, those signals are headed outward from Earth but they are so weak that the background "static" completely downs them out. Hearing them would be like listening for a pin drop sound while standing next to a jet aircraft with the engines run up.
But if we send a messages (with the above content) at a VERY slow data rate and build a special and very powerful transmitter, perhaps a laser and many millions of watts of power and aimed to directly are a target planet, the signal might be detectable over interstellar distances.
We will probably never make contact with actual physical space aliens. The distances are to great to travel but making contact via messages and signals might work. Let's say we decided to build a huge transmitter and send the above message to closest 10 million stars. This might be a distance out to 1,200 light years. This would be only a small part of the milkyway galaxy but it is about as far as you could ever hope to communicate. And even so we are talking about an enormous transmitter. There is a small chance that one of the stars might be inhabited and they could reply. So maybe, two thousand years after sending those prime numbers we get a return signal. With a 2,000 year lag time the conversation will advance very slowly. I think it is best to send longer messages. Perhaps the primes as an "attention" getter followed by quite a lot more real data about our culture and biology. We can hope they send the same thing back.
We guess: If we can only transmit out to 1,000 light years, then we may not ever contact anyone. The 2,000 year long experiment would likely have a negative result.
Since we have had ‘radio' (ca. 1910) this means that ANY signals will have at most reached 108 light years away.
Even if races IMMEDIATELY flew in our direction from say Sirius (8.6 LY away) AND could fly at light-speed, they would have arrived around 1927–8 at the earliest. Now this assumes that Sirians had light-speed travel - it is at best hypothetical.
At our current fastest speed it would take us 140,000 years to reach Proxima Centauri, which at 4,2 LY away is less than half the distance to Sirius.
Let's say at best, the Sirians could fly at 0.05 Light speed. That means the would have set out in 1919 (roughly) and would take 172 more years to reach us which means they would arrive in 2091.
Even if, against all odds, Centaurans were coming at the same speed, (and the chances of the nearest star having a civilisation at the same time as us, advanced enough to reach us at 0.05 light-speed), assuming they picked up Marconi's first radio waves, they would have arrived at best in 1998–9.
So saying something now is a) superfluous and b) nothing I want/need to do.
Thanks for asking. You must have seen my qualifications of Xenolinguistics and Xenopsychology. Unfortunately I'm only competent with hermit crabs at the moment.
I would have to hire a panel of linguists to consult with because the nature of words can make this a no-win situation. If I say "We come in peace." That might translate to "We're coming to pacify" Or "We're coming to bring order" if the receiving linguist interprets our sentiment or syntax while in a defensive mindset. Who knows what negative cultural experience that might evoke to them.
And even the seemingly innocuous "We're here to help!" accompanied by a smile can seem ominous if the memetic association of the receiving species links us to the Interstellar Revenue Service.
I would prefer to send send an unambiguously beautiful image. Something that projects the desired vibe like a child hugging a bunny. Until then I'd vote that we hold off on the project.
"Madame, why is the vicar hiding behind your settee and where are his trousers?"
That should pique Squabdwxx's interest.
Help, we are on a planet that is run by idiots .